Distributed key secret for rewritable blockchain

Abstract

A system includes circuitry for rewriting blockchains in a non-tamper-evident or tamper-evident operation using a key secret held in portions by multiple individually untrusted parties. The blockchains may include a series of blocks secured by integrity codes that may prevent non-tamper-evident rewrites by non-trusted parties that are not in possession of the key secret or individually-untrusted parties in possession of only a portion of the key secret. In some cases, multiple individually-untrusted parties may combine their portions into the key secret. As a group, the multiple individually-untrusted parties may perform non-tamper-evident operation with respect to at least one integrity code within the blockchain.

What is claimed is: 
     
       1. A method including:
 at rewrite circuitry:
 receiving a first portion of a key secret via a key secret exchange protocol; 
 combining the first portion with at least a second or a third portion of the key secret to obtain the key secret; and 
 using the key secret, performing at least a validity-preserving rewrite to a selected block of a data-tamper-protected blockchain, wherein the validity-preserving rewrite is implemented by substituting the selected block with a second block with different data content that produces the same or an equivalent integrity output. 
 
 
     
     
       2. The method of  claim 1 , where:
 the first portion is controlled by a first individually-untrusted party; and 
 the second portion is controlled by a second individually-untrusted party different from the first portion. 
 
     
     
       3. The method of  claim 2 , further including combining the first portion with at least the third portion of the key secret to support a non-tamper-evident rewrite to the data-tamper-protected blockchain and the third portion is controlled by a third individually-untrusted party different from the first portion. 
     
     
       4. The method of  claim 1 , where:
 combination of the first and third portions without the second portion is sufficient to support a non-tamper-evident rewrite to the data-tamper-protected blockchain; and 
 combination of the second and third portions without the first portion is insufficient to support the non-tamper-evident rewrite to the data-tamper-protected blockchain. 
 
     
     
       5. The method of  claim 1 , where combining the first portion with a second portion includes executing a key exchange operation that prevents disclosure of content of the first and second portions. 
     
     
       6. The method of  claim 1 , further including:
 combining at least the first and third portions to exceed a granting threshold and obtain a granting key secret; and 
 responsive to obtaining the granting key secret, assigning at least a key secret portion to an untrusted party. 
 
     
     
       7. A method including:
 at rewrite circuitry:
 obtaining a number of key secret portions; 
 combining the number of key secret portions,
 the combining responsive to an event,
 the event including the number of key secret portions exceeding a predetermined threshold, 
  the predetermined threshold including a threshold for validity-preserving rewrites; and 
 
 the combining executed to obtain a rewrite key secret; and 
 
 performing a validity-preserving rewrite to a selected block of a data-tamper-protected blockchain,
 the performing responsive to obtaining the rewrite key secret, and 
 the performing including determining new content for the selected block using the rewrite key secret, 
 wherein the validity-preserving rewrite is implemented by substituting the selected block with a second block with different data content, including the new content, which produces the same or an equivalent integrity output. 
 
 
 
     
     
       8. The method of  claim 7 , where:
 a first portion of the number of key secret portions is controlled by a first individually-untrusted party; and 
 a second portion of the number of key secret portions is controlled by a second individually-untrusted party different from the first portion. 
 
     
     
       9. The method of  claim 8 , further including combining the first portion with at least a third portion of the number of key secret portions to support a non-tamper-evident rewrite to the data-tamper-protected blockchain and the third portion is controlled by a third individually-untrusted party different from the first portion. 
     
     
       10. The method of  claim 7 , where:
 combination of a first and a third portions of the number of key secret portions without a second portion of the number of key secret portions is sufficient to support a non-tamper-evident rewrite to the data-tamper-protected blockchain; and 
 combination of the second and third portions without the first portion is insufficient to support the non-tamper-evident rewrite to the data-tamper-protected blockchain. 
 
     
     
       11. The method of  claim 7 , where combining a first portion with a second portion of the number of key secret portions includes executing a key exchange operation that prevents disclosure of content of the first and second portions. 
     
     
       12. The method of  claim 7 , further including:
 combining at least a first portion and a third portion of the number of key secret portions without a second portion of the number of key secret portions to exceed a granting threshold and obtain a granting key secret; and 
 responsive to obtaining the granting key secret, assigning at least a key secret portion to an untrusted party.